In general, when a pressurized fluid is supplied at a desired preset pressure from a pressurized fluid supply source to a pressurized fluid-driven apparatus, a pressure reducing valve is installed between the pressurized fluid supply source and the pressurized fluid-driven apparatus. The pressure reducing valve is operated such that the pressurized fluid on the primary side, which is supplied from the pressurized fluid supply source, is subjected to pressure reduction to a predetermined pressure suitable for the pressurized fluid-driven apparatus connected to the secondary side, and the fluid is supplied to the secondary side.
A pressure reducing valve, which has been suggested by the present applicant, is shown in FIG. 13.
The pressure reducing valve 1 comprises a main body unit 4 formed with a primary port 2 used to make connection on the side of a pressurized fluid supply source and a secondary port 3 used to make connection on the side of a pressurized fluid-driven apparatus, a bonnet 6 integrally coupled to the main body unit 4 and including a spring member 5 formed therein, and a handle 7 provided rotatably on an upper portion of the bonnet 6.
A central exhaust port 8 is formed at one side surface of the main body unit 4. The central exhaust port 8 functions as a bleed port for discharging an excessive amount of the pressurized fluid supplied from the primary port 2 to the atmospheric air, and it is also used as an exhaust port for discharging the pressurized fluid on the secondary side at a pressure higher than a preset pressure to the atmospheric air.
A first diaphragm 9, a second diaphragm 10, and a third diaphragm 11 are provided to extend at the inside of the main body unit 4. Those provided between the first diaphragm 9 and the second diaphragm 10 include a first diaphragm chamber 12 which communicates with the secondary port 3 via a first passage 12a, a nozzle back pressure chamber 13 which is formed separately from the first diaphragm chamber 12, and a flapper 14 and a nozzle 15 which perform seating operation or make separation from each other in accordance with an action of the pressurized fluid introduced into the nozzle back pressure chamber 13.
A second diaphragm chamber 16, which communicates with the central exhaust port 8, is provided between the second diaphragm 10 and the third diaphragm 11. On the other hand, a third diaphragm chamber 17 is provided under the third diaphragm 11. A communicating hole 18 for communicating the second diaphragm chamber 16 with the third diaphragm chamber 17 is formed through the third diaphragm 11. A valve plug 19 is provided so that its one end engages with the communicating hole 18. The valve plug 19 is in a state of being urged upwardly by the aid of the resilient force of a spring member 20. A communicating passage 21 between the primary port 2 and the secondary port 3 is opened or closed when the valve plug 19 makes separation or seating with respect to a seat section. A second passage 22 for communicating the primary port 2 with the nozzle back pressure chamber 13 is formed in the main body unit 4.
The operation of the pressure reducing valve 1 will be schematically explained below.
The pressurized fluid is supplied from the primary port 2 in a state in which the nozzle 15 and the flapper 14 are separated from each other by a predetermined spacing distance without exerting the resilient force of the spring member 5. The pressurized fluid passes through the second passage 22, and it is introduced into the nozzle back pressure chamber 13. The pressurized fluid passes through the gap between the nozzle 15 and the flapper 14, and it is introduced into the first diaphragm chamber 12. The pressurized fluid, which has been introduced into the first diaphragm chamber 12, passes through the first passage 12a, the third diaphragm chamber 17, and the communicating hole 18 of the third diaphragm 11, and it is bled to the atmospheric air via the central exhaust port 8.
The handle 7 is rotated in a predetermined direction so that the flapper 14 is pressed downwardly by means of the resilient force of the spring member 5, in the foregoing bleeding state in which the excessive amount of the pressurized fluid passes through the secondary side and it is discharged from the central exhaust port 8 to the atmospheric air. Thus, the nozzle hole of the nozzle 15 is closed. The pressurized fluid, which is supplied from the primary port 2, passes through the second passage 22, and it is introduced into the nozzle back pressure chamber 13. Accordingly, the pressure (nozzle back pressure) in the nozzle back pressure chamber 13 is increased. The second diaphragm 10 is pressed downwardly in accordance with the action of the nozzle back pressure. The second diaphragm 10, the third diaphragm 11, and the valve plug 19 are displaced downwardly in an integrated manner, and the valve plug 19 is separated from the seat section. Thus, the primary port 2 is communicated with the secondary port 3.
As a result, the primary pressure is reduced in accordance with the pressure-regulating action of the third diaphragm 11, and the reduced pressure is supplied to the pressurized fluid-driven apparatus connected to the secondary side.
When the secondary pressure is increased to be not less than a preset pressure, then the first diaphragm 9 and the third diaphragm 11 are pressed upwardly, and the valve plug 19 is seated on the seat section. Further, the third diaphragm 11 is separated from the one end of the valve plug 19, and the communicating hole 18 is opened. Therefore, the pressurized fluid having a high pressure on the secondary side is discharged to the atmospheric air from the central exhaust port 8 via the communicating hole 18.
In this case, the pressurized fluid in the nozzle back pressure chamber 13 passes through the gap formed between the nozzle 15 and the flapper 14 in accordance with the action of upward movement of the first diaphragm 9. After that, the pressurized fluid passes through the secondary side, and it is discharged to the atmospheric air from the central exhaust port 8. Therefore, it is impossible to quickly decrease the nozzle back pressure. As a result, a problem arises in that it is impossible to improve the response speeds of the second diaphragm 10 and the third diaphragm 11 to be displaced in accordance with the action of the nozzle back pressure.
An object of the present invention is to provide a pressure reducing valve which makes it possible to quickly decrease the nozzle back pressure when the secondary pressure is increased to be higher than a preset pressure, so that the response speed is increased, and which makes it possible to further improve the exhaust characteristics (relief characteristics) of the pressurized fluid on the secondary side.